Communication systems typically include a plurality of communication units, such as mobile or portable radio units, dispatch consoles and base stations (sometimes called base site repeaters) that are geographically distributed among various base sites and console sites. The radio units wirelessly communicate with the base stations and each other using radio frequency (RF) communication resources, and are often logically divided into various subgroups or talkgroups.
Communication systems are often organized as trunked systems, where the RF communication resources are allocated on a call-by-call basis among multiple users or groups. Wide-area trunked systems are sometimes organized into a plurality of “zones,” wherein each zone includes multiple sites and a central controller or server (“zone controller”) for allocating communication resources among the multiple sites. The zone controller(s) may reside within a single device or multiple devices and may be located at a fixed equipment site or may be distributed among various base sites. The RF resources may comprise, for example, narrow band frequency modulated channels, time division modulated slots, carrier frequencies, frequency pairs, or generally any medium for communicating information, such as voice, video, or data traffic (“payload information”) or control signaling (“control information”) to and from participating communication devices over wireless link(s).
Traditionally, the base sites and console sites were linked via a circuit-switched architecture, through dedicated or on-demand circuits to a central radio system switching point (“central switch”). The circuits providing connectivity to the central switch required a dedicated wire for each endpoint (e.g., base site or console site) whether or not the endpoint was participating in a particular call.
More recently, communication systems are beginning to use packet-switched technology where information that is to be communicated between endpoints is divided into packets and transported by various routers forming an Internet Protocol (IP) network. Packet-switched networks, sometimes called “connectionless” networks, are considered to be more efficient than circuit-switched networks because they allow for dynamic bandwidth allocation to participating devices on an as needed basis.
Due to the “connectionless” nature of packet-based networks, it is possible to over-subscribe certain links., including, but not limited to, inter-zone links that are leased by communication system customer(s). Generally, in any packet-based system, over-subscription of link(s) causes delays in transport of IP packets that adversely effect the quality of service of the network. Understandably, customers demand a certain quality of service and are more willing to occasionally queue (or “busy”) inter-zone calls due to insufficient resources than to pay extra recurring costs to overprovision these links to accommodate peak traffic loads. The problem is exacerbated in very large systems that may include hundreds of zones and hundreds of inter-zone links. Accordingly, there is a need for a method of call control in a packet-based communication system that provides for establishing calls over shared links of an IP network without exceeding available bandwidth.
One manner of addressing these needs is described in related U.S. Pat. No. 6,847,827, wherein reservations of bandwidth are statically established (i.e., pre-determined) for certain links by a first host device (e.g., zone controller) on behalf of at least a second host device (e.g., base station) that may require use of bandwidth. The reservations of call units are established using standard ReSerVation Setup Protocol (RSVP) signaling, prior to receiving any call requests, using multicast group address(es) that are never used for actual calls. If the zone controller receives a call request, it grants the request if there are sufficient reserved call units to support the call, in which case it forwards a different multicast address (i.e., different from the address(es) used to make the reservations) to participating endpoints and the call may proceed using that multicast address.
The present application provides an alternative manner of addressing the stated needs, whereby reservations of bandwidth for certain links are established dynamically (on a call-by-call basis) by host device(s) incorporating a reservation proxy function. The method provides for the host devices (hereinafter “reservation proxy elements”) to obtain reservations of call units using RSVP signaling using multicast group address(es) that are used for actual calls. Advantageously, the method may provide for limiting the scope of RSVP signaling to inter-zone links to minimize signal delays and the consumption of site bandwidth.